Flexible non-woven sheet material and method of making the same



United States Patent 3,458,387 FLEXIBLE NON -WOVEN SHEET MATERIAL ANDMETHOD OF MAKING THE SAME Stuart P. Suskind and Roy D. Goodwin, Raleigh,N.C., assignors t0 Monsanto Company, St. Louis, Mo., a corporation ofDelaware No Drawing. Filed June 14, 1966, Ser. No. 557,373 Int. Cl. D04h1/46; B32b 5/22 U.S. Cl. 161154 Claims This invention relates to aflexible non-woven sheet material. More particularly, this inventionrelates to a non-woven sheet material having uniform density andimproved dimensional stability which make it a useful substrate forpreparing synthetic leather products. Also, the invention relates to amethod for improving the Webforming properties of the staple fibersemployed to produce a heat-retracted, non-woven sheet material.

Loosely matted synthetic fibers have been compacted by severalmechanical processes in recent years to prepare non-woven sheetmaterials. These non-woven fabric structures derive their density andstrength from the coherence obtained from interfiber entanglement.Therefore, the fibers must be interlaced with respect to each other inorder to achieve the interfiber cohesion necessary to provide thestrength required for most non-woven products. The interfiberentanglement is generally accomplished by penetrating the loosely cardedstaple fibers with a multiplicity of needles provided with hooked pointsor barbs. To obtain optimum carding and needling of the fibers, acertain amount of fiber crimp is essential. However, in the preparationof fibrous webs from selfcrimping or heat shrinkable fibers forapplications where needle marks are objectionable, it is desirable todelay complete development of the crimp until after the needlingoperation. The subsequent crimp will further consolidate the web anddiminish the needle-punch marks.

Although the use of heat shrinkable fibers to prepare needle-punched,retracted non-woven webs is well known, several problems are encounteredin the web formation and needling processes with fibers of this type.Because of the absence or low degree of fiber crimp possessed by thesefibers prior to development of the latent crimp, thin batts preparedfrom heat-shrinkable fibers are often weak and poor in uniformity andcohesion. This result is compounded by the spreading of the uncrimpedfibers during the needle-punching operation and the accompanying lack ofuniform fiber entanglement.

Several attempts have been made in the past to improve the carding andneedling characteristics of uncrimped staple fibers. One approach towardsolving this problem has been to employ a special-type needle to reducethe fiber spreading. Another method has been to admix or blend crimpedfibers with the uncrimped fibers to reduce their propensity to spreadduring needling. Another method has been to employ woven supportingscrims which are either incorporated permanently or removed afterneedling also is well known while these prior methods have somewhatimproved the web cohesion and needling behavior of uncrimped fibers,they have not completely solved the problem. Therefore, it would behighly desirable to provide a simple and economical method for iceproducing an improved non-woven fabric structure from self-crimpingfibers. Self-crimping fibers are those fibers having the ability toretract in length principally through curling or coiling when heated orchemically treated to impose a crimped condition.

With the foregoing in mind, it is an object of the present invention toprovide a method for producing a thin non-woven fabric structure whichhas uniform density and improved strength from self-crimping fibershaving little or no crimp.

Another object of the present invention is to provide a method forimproving the needling characteristics of webs formed from looselymatted staple fibers which have little or no crimp.

A further object of the present invention is to provide a method forstabilizing the spreading propensity of synthetic fibers having a lowdegree of interfiber coherence while undergoing needle punching in aloosely matted web.

Yet another object of the present invention is to provide a flexiblenonwoven fabric structure having uniform density and excellent drape.

Still another object of the present invention is to provide a flexiblenon-woven fabric structure formed from loosely matted synthetic staplefibers which are stabilized dimensionally during needle punching withoutadversely affecting the shrinkage properties of said fibers or thebending length of said fabric structure.

Other objects and advantages of the invention will be apparent from thedescription to follow.

The above objects have been accomplished in accordance with the presentinvention which is a non-woven fabric structure comprised of amicrofibrous web sandwiched between layers of coarser fibers which areinterlaced in a cohering relationship with respect to each other throughthe microfibrous web by needle punching to entangle the coarser fibersand microfibers. The microfibers are less than 1 denier, and preferablyless than 0.5 denier and the coarse fibers are greater than 1 denier,preferably 1.5 denier and above. In the production of non-woven fabricstructures for use as substrates in the manufacture of oromericmaterials such as synthetic leather, it has been discovered that a verydense web is essential in obtaining a suitable product. It is well knownthat dense webs are prepared from heat-shrinkable fibers which areformed into coherent batts by a needle-punching or similar process andthen subjecting the batt to sufiicient heat to shrink the fiber therebysubstantially increasing the density of the web. Since the fiberspreferably are not retracted until after the needle-punching operation,they possess only a slight amount of interfiber coherence. As statedearlier, the needling or similar fiber entanglement process causes thesubstantially straight fibers to separate and spread to the extent thatuniform density of the Web is difiicult to be controlled.

According to the present invention the spreading of the fibers duringthe fiber entanglement step is controlled by the microfiber web whichdoes not spread substantially because of the high degree of interfiberentanglement and accompanying frictional forces possessed by themicrofibers. Microfiber webs can be prepared in a number of ways byconventional processes such as carding, deposition from an air stream orby paper-making techniques. Preferably, the microfiber webs are made bythe processes disclosed in copending application Ser. No. 464,411 nowPatent No. 3,317,954, and Ser. No. 464,477, filed June 16, 1965, whereinthe microfibers are collected in continuous webs on a foraminous belt.The Webs formed by these processes have excellent dimensional stabilityand are extremely flexible, which are two essential properties requiredof leather-like products.

Heretofore, woven fabrics or bonded non-woven fabrics have been employedin some instances to stabilize carded staple fibers during theneedle-punching prouess. Because of the high degree of flexibility whichmust be maintained when manufacturing leather-like products, the knownreinforcement scrims have been found to be unsatisfactory. On the otherhand microfibrous webs provide the desired amount of dimensionalstability to prevent the outer layers of coarser fibers from spreadingand also add substantially to the density of the fabric structurewithout affecting adversely the flexibility or drape properties of thefinal product.

The outer layers of the P oduct of this invention are prepared from anytype of fibers having the capability to shrink into a consolidated webafter the fibers have been compacted by a preferred fiber entanglementprocess. For example, the fibers may be an acrylic/elastomeric compositeof the type disclosed in copending application Ser. No. 369,359 filedMay 21, 1964; texturized unrelaxed nylon, polyester or acrylic fibers;high shrinkage acrylics, modacrylics, polyester, polyolefins orpolyamides; bicomponent acrylic fibers; unrelaxed polyvinylchloridefibers; nylon conjugate fibers; or, blends of the above heat retractablefibers. In addition, minor amounts of cardable natural fibers may beemployed as blends with the above synthetic fibers. Theacrylic/elastomeric composite fiber i highly preferable because of itsability to shrink and consolidate the fibers into a dense, flexible Webhaving a suitable amount of elasticity.

The relative amounts of coarse fibers and microdenier fibers may bevaried considerably depending upon the dimensional stability desired tofacilitate compacting of the coarse fibers prior to shrinkage of thecompacted fibers. Obviously, some fibers have a greater propensity tospread than others and therefore are more difficult to control. It hasbeen found that for most heat-retractable fibers a microfiber webcomprising from 5 to weight of the composite structure provide adequatestrength to insure that uniform density is maintained. The microfibersbeing the minority constituent are disposed near the center with respectto the broad surfaces of the composite structure to prevent them fromemerging to the surface and imposing their influence on the surfacecharacteristics of the finished sheet material.

The product of this invention may vary in thickness from a very thinmaterial of about mils to about 100 mils, but preferably from about 50to 70 mils after the fibers have been compacted and shrunk. The layeredcomposite web, which has been compacted preferably by a needling processwherein the needles penetrate the three layers to reorient part of thefibers, should have the capability of shrinking at least 20 percent inplanar area, and preferably more than 50 percent. Therefore, it ishighly desirable that the web of fibers be consolidated to a uniformdensity prior to heat-retraction of the uncrimped fibers and that thereinforcing scrim which facilitates better web consolidation iscomprised of a substrate that does not restrict, appreciably, theshrinkage of the heat-retractable web in order to produce a flexiblesheet material having uniform density. Shrinkage of the web may beaccomplished in hot Water, steam or dry heat. After the web has beenshrunk the proper amount, it may then be impregnated with an aqueous orsolvent based synthetic elastomer and dried by a suitable technique, ifdesired, to produce a synthetic suede leather having excellentproperties. The impregnated web may be buffed and brushed to raise fiberends at the surface and to improve the bond and surface appearance.Optionally the impregnated web may be finished by dyeing or overlappingsoil repellents and the like.

The product of this invention is an excellent substrate material for afinished synthetic leather product. The finishing or coating process mayconsist of applying a light-weight woven or non-woven scrim to adddimensional stability and strength; coating with a polymeric material;and surface coating this with a thin layer of a polymer to enhanceabrasion resistance, durability and light stability.

The following examples illustrate the improvement achieved from theemployment of a microfiber web in the preparation of needle punched websof heat-shrinkable fibers.

Example I A carded batt weighing 4.23 oz./yd. was prepared from 2.6denier per filament, 1.5 inch polyester-polycarbonate conjugate staplefiber capable of developing a crimp on relaxation with heat. One-half ofthe fiber crosssection was 100 percent polyethylene terephthalate andthe other half was a blend of 94 percent polyethylene terephthalateblended in the melt with 6 percent polycarbonate. The batt was needlepunched once on each side for a total of 3,000 punches per square inchon a conventional needle loom. The needle-punched web had a density of0.068 gm./cc. The web was then placed in a hot water bath (95 C.) forseveral minutes to retract the fibers. The reduction in planar area ofthe web was 35 percent resulting in a web.

Example II A needle-punched web as in Example I was repeated with amicrodenier acrylic web weighing 1.0 oz./yd. placed between the twopolyester-polycarbonate staple batts prior to needle punching. Theneedle-punching step in Example I was repeated with a noticeablereduction in web spreading and visible needle marks which wereexperienced in the web from the preceding example. The web was retractedin a hot water bath (95 C.) with an accompanying area loss of 30percent.

The web had a density of 0.084 gm./cc. before being heat retracted and0.141 gm./cc. afterwards. Thus, the presence of the microfiber websubstantially increased the density of the Web before and after heatretraction. Because of the reduced spreading during the needle-punchingstep, the web containing the microfiber web was denser and moreuniformly consolidated. The retracted web had a bending length of 1.44inches which indicates that the microfiber web does not adversely affectthe drapeability thereof.

Examples III-IV These webs were constructed in accordance with theprocedures used in Examples I and II except a different combination offibers as shown in the following table were employed.

The data in the table below illustrates the improved strength anddimensional stability achieved by employment of a microfiber web. Theoutstanding improvements imparted to the webs by the microfiber interlaywas the achievement of improved strength and web cohesion without anyappreciable loss in flexibility or drape.

DEAD LOAD EXTENSION Bending Time Lu, AL ALX100 length Sample (1 width)(min.) (inch) (inch) Lu (inch) Polyester-polycarbonateneedle-punched-Test direction:

acliine 1. 8 45. 1. 48

2.05 1.75 Transverse 6. 85 6. 85

Polyester-polycarbonate acrylic microfiber (AMF) web sandwich-Testdirection:

Maclnn Needle-punched-Test direction:

Transverse Dynel staple needle-punched 'lest direction:

Machine Transverse Dynel-AMF-Dynel needle-punched -Test direction:

Acrsfiic tkzlonjugate (80%), acrylic copolymer needle-punched-Testdirection:

c ne

Transverse amp Acrylic conjugate (80%), acrylic copolymer (20%) with AMFneedle-punched-Test direction: Machine 1g Acrylic conjugate (80%),acrylic copolymer (20%) with polyvinylchloride microfiber web-Test'rection:

Machine 5 5 0. 45 15 5 0. 50 N ecdle-punel1ed-Tcst direction:

Transverse 5 5 1. 2 15 5 1.

l A weight of 161 gms. was hung freely from a one inch width sample.

2 Original length.

3 Percent elongation.

4 Bending length was measured in accordance with ASTM-D-1384-64.

5 High shrinkage fiber comprised of a copolymer of acrylonitrile andvinyl chloride in approximately a 60/40 ratio.

AMF, acrylic microdenier fiber.

A comparison of the data obtained from webs without the microfibers andsimilar webs reinforced with the microfibers in the above tableindicates that the microfibers impart a substantial amount of strengthto the web structures. Particular attention should be given to the factthat the bending length of the sheet material is not significantlyincreased by the microfibers.

What is claimed is:

1. A flexible non-woven sheet material having a uniform density which iscomprised of two layers of unretracted synthetic staple fibers beingentangled with respect to each other through a layer of microfibersdisposed between said layers to form a composite structure.

2. The product of claim 1 in which the staple fibers are at least 1denier per filament and the microfibers are less than 1 denier perfilament.

3. The product of claim 2 in which the staple fibers are self-crimpingwhen heated to effect at least a 20 percent area loss of said sheetmaterial.

4. The product of claim 2 in which the microfibers possess a high degreeof interfiber entanglement which improves the dimensional stability anddensity of the sheet material.

5. The product of claim 2 in which the staple fiber entanglement throughthe microfibers is accomplished by needle punching.

6. The product of claim 2 in which the microfibers comprise from about 5to 15 percent by weight of the composite structure.

7. The product of claim 6 further characterized by impregnation in anelastomeric composition.

8. The product of claim 7 further characterized by a polymeric surfacecoating.

9. A method for improving the web-formation properties of self-crimpingsynthetic fibers which comprises:

(a) disposing a batt formed from the fine denier fibers having a highdegree of interfilamentary cohesion between two layers of coarsersynthetic fibers to form a composite structure, and

(b) needle punching the composite structure to effect an interlacing ofthe coarser fibers through the fine denier fibers in a coheringrelationship with each other to provide a flexible web having uniformdensity and improved dimensional stability.

10. The method of claim 9 in which the needle-punched web is shrunk atleast 20 percent to effect densification thereof by retractnig thecoarser staple fibers in a heated environment.

References Cited UNITED STATES PATENTS 3,016,599 1/1962 Perry 161-1693,206,351 9/1965 Smith 161-154 X 3,245,863 4/ 1966 Sonnichsen et a1.161-72 3,317,954 5/ 1967 Crompton 65-8 X 3,321,356 5/1967 Merriman eta1. 28-72.2 X 3,373,455 3/1968 Kaplan 161-166 X 3,388,028 6/1968Alexander 161-156 3,400,042 9/1968 Riedesel 161-170 X ROBERT F. BURNETT,Primary Examiner R. L. MAY, Assistant Examiner US. Cl. X.R.

1. A FLEXIBLE NON-WOVEN SHEET MATERIAL HAVING A UNIFORM DENSITY WHICH ISCOMPRISED OF TWO LAYERS OF UNRETRACTED SYNTHETIC STAPLE FIBRS BEINGENTANGLED WITH RESPECT TO EACH OTHER THROUGH A LAYER OF MICROFIBERSDISPOSED BETWEEN SAID LAYERS TO FORM A COMPOSITE STRUCTURE.